Interesting failure NRA-UK report

[butlersrangers]

This 'catastrophic failure' of a Norwegian Krag occurred in Great Britain at a practice match in the Spring of 2014. It was investigated by the NRA-UK. The 23 page report was posted today on the Military Surplus Collectors Forum (under Krag rifles).

The Norwegian Krag action (#32513) was of 1897 Steyr vintage. A Norwegian match barrel was installed circa 1950 and the rifle has been in routine use and well maintained. Nicks and alterations to the action receiver ring and threads led to suspicions regarding the installer's competency.

The 'home loads' (reloads) used Norma brass, 140 grain bullet, and 34.4 grains of Accurate 2520. (This load appears just above a 'starting load' and well below Max. in one Accurate Arms table, I found). The rifle came apart on the fourth shot. The 'shooter', a neighboring 'shooter', and a spectator were injured and required hospital treatment (surgery for two and OP for the third).

The NRA-UK report noted 'grossly deformed necks' on some of the 'homeloads', which indicated improper setting of equipment. They displayed one of the fired cases, which looked normal. However, IMHO, the photo of a deformed loaded case in a Wilson gauge, appears to show a possible head-space problem, caused by excessive case length or poor adjustments. (I wish the report gave more attention to the dimensions of the fired cases and case length of the deformed necks).

Some parts of the destroyed Krag-Jogensen could not be found. The NRA-UK found no clear definite cause and called it: "A single overload event". If I understand the report's conclusion correctly, they attributed the failure to an excessive load or latent defect in the re-barreled rifle.

(The excessive pressure could have been an under-load detonation, an excessive pressure over-load, or something related to the 'funny' case necks).

[butlersrangers]

Hey, that single bolt lug held and we have visual evidence that Norwegian Krags have left-hand barrel threads. I bet our shooters can come up with a better analysis of this accident than the 'Brits' did!

(Those distorted case necks must cause a problem with neck-bullet tension. Deformed case neck pics):

[cdagnese]

Detonation is a very plausible cause here. Fast powders and low case density are a dangerous thing in rifle calibers. Too large a diameter of projectile could also cause this.

A note about the Brits. There's a story going around the FAA about the Bits. They were looking for a way to test the windshields for their high speed trains. They asked the FAA to borrow the "Chicken Gun" that we use to test aircraft windshields. It actually shoots chicken carcasses at the windshield. Well, the Brits, using the Chicken Gun, busted just about every windshield the had and sent a report to the FAA for review. They couldn't understand why all their windshields were breaking. After the FAA read the report, they sent the Brits one recommendation. "Thaw out the chickens before you shoot them".

[Parashooter]

Hey, that single bolt lug held . . .

Single lug? (The usual Norwegian arrangement has two, no?)

[butlersrangers]

Yeh, one forward lug, a bolt guide rib (fitted to make contact with the receiver, unlike U.S. Krag bolts), and the bolt handle root.

I guess my point was: The bolt was not the weakest link.

[Bernt]

Hi guys, just posted this on the Milsurp forum. I'll post it here as well. Just some background info from Norway. Krags rarely blow up, but when they do, this is the usual pattern.

In the 1970's the norwegian Krag ammo was downloaded to a preassure of 2800 BAR (from originally 3100 BAR). The reason was that some Krags started to develop cracks. These rifles had shot maybe tens of thousands of shots with metal fatiqe on certain spots as a result. The cracks are usually found in the lower right corner, near where the locking lug engages the receiver, and in the upper left corner by the extractors supportspring. On Kongsberg Krags these corners are sharp (90`) , while the Steyr Krags have rounded corners, and are considered stronger. The sharp corner is a more likely starting point for a crack than a rounded corner.

As they say: "Allways have a competent gunsmith check any old gun before you fire it".

Faulty ammo can blow up any rifle. And this Krag blew up in the usual pattern. The cut for the extractor is the weakest spot around the case, and when it burst, this is where the gasses go. The extractor and top of the receiver ring is blown off as a result.

This link to a norwegian forum shows a Krag that were blown up on purpose. The guy loaded a full case of N110 or N340, tied it to a tree, and pulled the trigger with a string.
It looks pretty much identical to the UK incident.

http://www.kammeret.no/forum/viewtopic.php?f=14&t=86653&sid=debd5878d18e0e7b53e76942bd577055&start=80

[madsenshooter]

It appears the fellow needs some reloading lessons. SEE is a possibility. Low charge, long and perhaps rough throat. The bullet stops for a millisecond, the powder keeps burning and pressure goes through the roof. 6.5 Swedish is notorious for this, not just in Krags, guys have blown up more than one Swedish Mauser with loads that were meant to take it easy on the old gun.

[FredC]

Looking at both fotos of the blown up guns I am wondering if the threaded ring did not fail first. Maybe the relatively soft barrel swelled splitting the ring and as the barrel moved forward after the ring split, the extractor pulled the rim till the rim/case failed. The American Krag is not particularly weak in the area of the cut. I just finished rebarreling an action and I was impressed with the strength in that area. The Brits may have been on to something when they mentioned the marks on the receiver. A pipe wrench applied there during rebarreling would make deep marks that would concentrate stress and drastically weaken it.

[butlersrangers]

I'm not an Engineer or Metallurgist, but IMHO, this mischief was caused by extreme high pressure gases (due to over-load, under-load detonation, bullet/throat problem, compromised cartridge case???) blowing out the case head and allowing the gases to enter the action. (Metal fatigue or flaws may have contributed, but, probably not necessary or root cause).

When rimless cartridges and their rifle actions 'blow up', they look kind of similar, with top of receiver ring and extractor gone, and other wreckage somewhat restrained by wood.

[kragluver]

Just to set the record straight, small charges of SLOW powder in rifle cases are what cause SEE. Fast powders should be used for reduced loads (e.g., 5744, 2400 or 4759, etc.). There is a lot of misinformation out there about SEE. Anyone interested should read Firearm Pressure Factors.